fs/9p: Fix race in initializing writeback fid

When two process open the same file we can end up with both of them
allocating the writeback_fid. Add a new mutex which can be used
for synchronizing v9fs_inode member values.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

4 files changed, 11 insertions, 0 deletions

diff --git a/fs/9p/v9fs.h b/fs/9p/v9fs.h
index bd8496db135b..89657e865162 100644
--- a/fs/9p/v9fs.h
+++ b/fs/9p/v9fs.h
@@ -130,6 +130,7 @@ struct v9fs_inode {
 #endif
         unsigned int cache_validity;
         struct p9_fid *writeback_fid;
+        struct mutex v_mutex;
         struct inode vfs_inode;
 };
 
diff --git a/fs/9p/vfs_file.c b/fs/9p/vfs_file.c
index 78bcb97c3425..3337d58d0fc5 100644
--- a/fs/9p/vfs_file.c
+++ b/fs/9p/vfs_file.c
@@ -90,6 +90,7 @@ int v9fs_file_open(struct inode *inode, struct file *file)
         }
 
         file->private_data = fid;
+        mutex_lock(&v9inode->v_mutex);
         if (v9ses->cache && !v9inode->writeback_fid) {
                 /*
                  * clone a fid and add it to writeback_fid
@@ -101,10 +102,12 @@ int v9fs_file_open(struct inode *inode, struct file *file)
                 fid = v9fs_writeback_fid(file->f_path.dentry);
                 if (IS_ERR(fid)) {
                         err = PTR_ERR(fid);
+                        mutex_unlock(&v9inode->v_mutex);
                         goto out_error;
                 }
                 v9inode->writeback_fid = (void *) fid;
         }
+        mutex_unlock(&v9inode->v_mutex);
 #ifdef CONFIG_9P_FSCACHE
         if (v9ses->cache)
                 v9fs_cache_inode_set_cookie(inode, file);
diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c
index 8a2c232f708a..c6cef2495f00 100644
--- a/fs/9p/vfs_inode.c
+++ b/fs/9p/vfs_inode.c
@@ -221,6 +221,7 @@ struct inode *v9fs_alloc_inode(struct super_block *sb)
 #endif
         v9inode->writeback_fid = NULL;
         v9inode->cache_validity = 0;
+        mutex_init(&v9inode->v_mutex);
         return &v9inode->vfs_inode;
 }
 
@@ -650,6 +651,7 @@ v9fs_vfs_create(struct inode *dir, struct dentry *dentry, int mode,
         /* if we are opening a file, assign the open fid to the file */
         if (nd && nd->flags & LOOKUP_OPEN) {
                 v9inode = V9FS_I(dentry->d_inode);
+                mutex_lock(&v9inode->v_mutex);
                 if (v9ses->cache && !v9inode->writeback_fid) {
                         /*
                          * clone a fid and add it to writeback_fid
@@ -661,10 +663,12 @@ v9fs_vfs_create(struct inode *dir, struct dentry *dentry, int mode,
                         inode_fid = v9fs_writeback_fid(dentry);
                         if (IS_ERR(inode_fid)) {
                                 err = PTR_ERR(inode_fid);
+                                mutex_unlock(&v9inode->v_mutex);
                                 goto error;
                         }
                         v9inode->writeback_fid = (void *) inode_fid;
                 }
+                mutex_unlock(&v9inode->v_mutex);
                 filp = lookup_instantiate_filp(nd, dentry, generic_file_open);
                 if (IS_ERR(filp)) {
                         err = PTR_ERR(filp);
diff --git a/fs/9p/vfs_inode_dotl.c b/fs/9p/vfs_inode_dotl.c
index 67c138e94feb..327c578c7ba6 100644
--- a/fs/9p/vfs_inode_dotl.c
+++ b/fs/9p/vfs_inode_dotl.c
@@ -245,6 +245,7 @@ v9fs_vfs_create_dotl(struct inode *dir, struct dentry *dentry, int omode,
         v9fs_set_create_acl(dentry, dacl, pacl);
 
         v9inode = V9FS_I(inode);
+        mutex_lock(&v9inode->v_mutex);
         if (v9ses->cache && !v9inode->writeback_fid) {
                 /*
                  * clone a fid and add it to writeback_fid
@@ -256,10 +257,12 @@ v9fs_vfs_create_dotl(struct inode *dir, struct dentry *dentry, int omode,
                 inode_fid = v9fs_writeback_fid(dentry);
                 if (IS_ERR(inode_fid)) {
                         err = PTR_ERR(inode_fid);
+                        mutex_unlock(&v9inode->v_mutex);
                         goto error;
                 }
                 v9inode->writeback_fid = (void *) inode_fid;
         }
+        mutex_unlock(&v9inode->v_mutex);
         /* Since we are opening a file, assign the open fid to the file */
         filp = lookup_instantiate_filp(nd, dentry, generic_file_open);
         if (IS_ERR(filp)) {